<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>flex布局</title>
    <style>
    /*     #flex{
            display: -webkit-flex;
            display: flex;
            flex-direction: row;
            justify-content: center;
            align-items:center;
        }
        #first{
            order:0;
        }
        #second{
            order:10;
            
        } */
        #container{
            background-color: grey;
            height: 500px;
            width: 500px;
            display: flex;
            align-items: center;
            justify-content: center;
        }
        .center{
            display: flex;
            align-items:center;
            justify-content: center;
        }
       .one{
           background-color: yellow;
           height:100px;
           width: 100px;
       } 
       #circle1{
           background-color: red;
           height: 20px;
           width: 20px;
           border-radius: 50%;
       }
    </style>
</head>
<body>
 <!--    <div id="flex">
        <p id="second">2</p>
        
        <div>3</div>
        <div>4</div>
        <p id="first">1</p>
    </div> -->
    <div id="container">
    <div class="one center">
        <div id="circle1"></div>
    </div>
</div>
</body>
</html>